Steam heating system



March 21, 1944. B, J [NGRAM 2,344,874

' STEAM HEATING SYSTEM Filed May 15, 1941 3 Sheets-Sheet -1 INVENTLOR Bernard J 079mm B. J. INGRAM March 21, 1944.

S TEAM HEATING SYSTEM Filed May 15, 1941 3 Sheets-Sheet 2 tllllllllllllllllllllll l INVENTOR Bernard J /n ram March 21, 1944. B ,NGR' M STEAM HEATING SYSTEM 3 Sheets-Sheet 3 Filed May 15 Patented Mar. 21, 1944 UNITED STATES PATENT OFFICE STEAM HEATING SYSTEM Bernard J. Ingram, Sewickley, Pa, assignor of one-fourth to Earl F. McConnell, Pittsburgh, one-fourth to James R. King, North Braddock, and one-fourth to Alexander Clydesdale, Jr., Mount Washington, Pa.

Application May 15, 1941, Serial No. 393,566

12 Claims.

, This invention relates to steam heating and is tor a method and apparatus employing steam as a heating medium wherein vacuum is employed to induce the flow of steam through the heating system.

The invention is primarily applicable to heating systems for use in buildings, particularly large buildings, but it is also applicable for other uses where steam is circulated through a heat exchange unit for the purpose of heating another fluid, either air or liquid. It may be used, for example, in maintaining the temperature of water in swimming pools. Since the invention is primarily applicable, however, for the heating of buildings, it will be specfically described in this connection.

Heating apparatus for buildings is commonly provided with a system of radiators, all of which are connected on oneside to a source of heat supply and which are connected on the opposite side with a discharge line through which used steam and condensate are returned to the boiler or power plant which supplies the steam. In the operation of such systems, the steam pressure is increased sufliciently above atmospheric pressure to overcome the frictional loss in the heating system. When the proper pressure for forcing the steam through the system has been determined, the system is operated to supply the steam at this fixed pressure. In some cases the steam is supplied continuously, resulting in the overheating of the building and the necessity for the tenants to individually regulate the heat. In other systems the steam is intermittently supplied to the radiators, the length of the on-andofi periods being varied according to the prevailing outside temperature. This results in nonuniform heating; in high peak demands for steam requirements, and does not at all times result in heat being supplied to the room at the particular time that a tenant may need it. Such systems, moreover, usually require the use of thermic traps at the discharge side of each radiator to prevent live steam from being'forced into the condensate lines and require the installation of orifice plates at various points in the system to assure a more uniform distribution of steam.

It is, of course, well-known that steam at pounds pressure or at atmospheric pressure is 212 F. By decreasing the pressure the temperature of the steam may be lowered so that with a vacuum of 25 inches of mercury the temperature, of steam is reduced to approximately 132 F. The present invention makes use of this fact and provides a method wherein during extremely cold periods steam entering the radiators is at 0 pounds or atmospheric pressure and as the weather becomes warmer the degree of vacuum is increased, correspondingly lowering the tem-. perature of the steam and thereby enabling the heat to be supplied to the radiators more or less constantly but at temperatures suited to the prevailing weather. This results not only in a substantial economy of operation due to the fact that the maximum demands of heat loads are always relatively low, but also due to the fact that more of the heat in the steam is made available. For example, in the pressure systems above referred to, the water condenses in the radiator and runs to the condensate lines at a temperature somewhere around 200 F., whereas with the present system the steam may be cooled as low as 132 before it is discharged as condensate and the difference is a direct saving. Such a system has other advantages as, for example, safety due to the fact-that if a leak develops in the system, atmospheric air is sucked from the room into the system rather than steam or hot water being forced under pressure into the room or wall space as occurs when pressure heating is used.

Attempts have heretofore been made to use sub-atmospheric pressures in the operation of heating systems but they have required expensive equipment, continuously operating pumps of large capacity, the necessity for accurately operating the thermic traps at the end of each radiator to prevent wasting steam, and they have lacked flexibility of control.

The present invention is an improvement over the invention disclosed in my co-pending application Serial No. 316,571, filed January 31, 1940. The invention may be more fully understood by reference to the accompanying drawings, in which- Figure 1 is a schematic diagram of a heating system embodying my invention for complete automatic operation by means of an outside temperature bulb;

Figure 2 is a sectional view of the steam control valve used in the automatic system of Figure 1;

Figure 3 is a sectional view showing the construction of one of the expansible chamber motors used in the automatic system;

Figure 4 is a plan view of one of the electric contact devices forming a part of the automatic system;

Figure 5 is a fragmentary view of a portion of the contact arrangement of Figure 4;

Figure 6 is a similar view of another part of the contact arrangement of Figure 4; and

Figure 7 is a partial view of a heating system showing a modified form of valve intended for use either with full manual operation or with automatic operation.

Referring first to Figure 1, 2 designates generally a heat exchange system comprising, for

example, a number of radiators 3. These radiators are connected on their inlet side with a,

steam supply pipe 4. They are each provided with outlet pipes 5 leadingto condensate return line B. In the condensate return line 6 is a float controlled trap I of conventional form in which the condensate collects until it has reached a predetermined depth when it is discharged into a discharge line 8 leading to a condensate collecting tank 9. Leading from the condensate tank 9 there may be a discharge pipe I in which is a pump ll. An outwardly-opening inwardlyclosing check valve I2 is provided on the discharge side ofthe pump I so as to permit water to be expelled from the system but prevent gases from flowing back through the pump into the system.

Shunted around the float-operated trap "I is a looped pipe l3 which connects into the pipe in advance of the trap 1 and connects into the pipe 8 on the dischargeside of the trap I. In this pipe I3 is a check valve !4 which is biased by weight l5 to normally remain open, this check valve being arranged to open inwardly and close outwardly. By adjusting the weight 15 the valve will close only when there is a predetermined differential of pressure on the opposite sides of the valve. V

Communicating with the pipe 8 is a suction line l5 that leads to' a vacuum pump ll. The vacuum pump is driven by an electric motor I8. In the pipe I 6, close to the pump !1, is an outwardly-opening inwardly-closing check valve I9. The pipe 20 leads from the suction line It to the top of the chamber 9 so as to equalize pressures in the chamber 9 and above the condensate discharge pipe 8 to prevent water or condensate being drawn into the suction pump l1. Likewise a suction equalizing pipe 2| leads from the condensate tank 9 to the pump I! so as to equalize pressure between the pump and the condensate tank 9 and prevent the vacuum from holding the Water in the pipe 9 and permit it to flow freely through the pipe Ill.

The motor I8 is controlled by an electromagnetically operated switch 22, there being an electromagnet or relay 23 for closing the switch while the spring 24 tends to open it. The steam inlet pipe 4 communicates with a manifold 25 in which is a valve. 26 which may be of the form shown in Figure 2. Connected to the inlet side of the valve 26 is a steam supply line 21 which may communicate with the boiler or with a steam supply service line. The valve 26, as shown in Figure 2, has an internal double ported valve with a double valve element 28 and an operating stem 23. The stem 29 is provided with opposed abutments 30 and with a terminal knob 3|. Between the opposed abutments 39 is the outer end of an arm 32, which arm is pivotally supported at 33 and has its opposite end 34 pivotally connected to the operating extension 35 of a Sylphlon or expansible chamber motor 36 which may be of any conventional form as, for example, that shown in Figure 3 in which the motor 35 comprises a housing v 31 with an expansible bellows 38 therein. Attached to one end of the bellows side of the check valve 43.

is a head 39 on which the operating extension 35 is secured. The other end of the bellows is fixed to the interior of the chamber 31. Pressure is communicated to the interior of the chamber 3'! through a pipe 40. The movement of the arm 32 under the influence of the motor is opposed by tension spring 4|.

The expansible chamber motor 35 with its pipe 40 communicates to a vacuum control pipe line 42 which leads from the pipe l6 adjacent the check valve IE! to the manifold 25. This line 42 has a check valve 43 therein which opens toward the steam supply manifold 25 and closes in a direction toward the pump H and the pipe 49 communicates with the pipe 42 on the pump The arrangement is such that when a predetermined degree of vacuum is reached in the pipe 42 it will be communicated through the pipe 40 to the Sylphon motor 35 causing the expansible element of said motor to contract, forcing the outer end of the arm 32 down to close the valve 25. When the vacuum in the pipe 42 decreases sufiiciently the spring 4! tends to lift the arm 32 and raise or open the valve 26.

Leading from the pipe 42 on the same side of the check valve 43 of the pipe 40 is another branch pipe 44 that communicates with a Sylphon motor or other expansible motor 45. This motor operates an arm 45 similarly to the arm 32, except that as shown-in Figure 1 the arm 46 is pivotally supported at one end instead of intermediate its ends so that an increase in the vacuum in the line 44 tends to draw the arm 46 upwardly and the spring 9! is arranged oppositely to the spring 45 and the motor 35. The arm 45 has a circuit closing brush 4'! at the outer end thereof which is adapted to be moved with the movement of the arm progressively over a series of contacts 48. As shown in Figures 4 and 6 the brush 4! preferably is in the form of a block 49 having an elongated contact 59 on the under-surface thereof and having a slot 5| therein through which the arm 45 passes, the slot allowing a certain amount of lost motion between the arm 45 and the brush. The contacts 48 are close together and the contact element 59 is of suflicient length that when the arm is at the lowermost of the series of contacts, all of the contacts of the series will be engaged, but as the arm moves up, the contacts will be progressively eliminated from the circuit.

Each contact in the series 48 is electrically connected with a corresponding contact 52 in the series of contacts 52 shown in Figure 1. These contacts 52 are similar in arrangement to the contacts 48, and thereis a brush 53 comprising a block 49 having a roller 50' which rides over these contacts 52, the block 49' having a slot 5| therein through which one end of an operating arm 54 extends. This arm is operatively connected with a Sylphon motor or other expansible chamber motor 55. The connection between the arm 54 and the brush 53 is also preferably a lost motion connection. The contacts 52 are shaped to overlap so that the roller 59' will not, over the range of contacts 52, ever be at a neutral point. It may at times simultaneously engage two, but never more than two, contacts. The contact device comprising the brush 53 and the seriesof contacts 52 has in addition at the upper end of the series of contacts 52 an extended contact 55 onto which the brush may ride after it has engaged the last one of the series of contacts 52. There may be any number of contacts 52 and 48' in the series. I prefer that there be about sixteen of these contacts.

The expansible chamber motor 55 is connected through a tube 51 with an outdoor bulb 58 containing temperature responsive fluid so that the brush 53 will be moved upwardly over its series of contacts 52 as th outside temperature rises and will move downwardly over the contacts 52 as the outside temperature drops.

The two expansible chamber motors 45 and 55 with the contact device which they operate constitute the control for the motor 18 which drives the pump H. The circuit for this control comprises current supply lines 59 and 65. There is a double pole switch at 6|. The wire 59 leads through the switch 6| to wire 62 that is connected to the arm 54, thereby conducting energy to the brush 53. The contacts 52 engaged by the brush 53 are in turn connected with the corresponding contacts 48 to be engaged by the brush 4?. From the brush 4'! and arm 45 there is a wire 63 which connects to one side of the magnet coil 23 of the relay switch 22. The other side of the electromagnet 23 is connected through wire 64 to the other side of the switch SI and the power line 59. Thus the arrangement is such that when the brushes 53 and 4'! are on corresponding contacts 52 and 48, respectively, the magnet 23 will be energized and the switch 22 will be operated to close the circuit to the a calibrated segment 58, one calibration of which I may give the outside temperature in degrees Fahrenheit and the other calibration of which may indicate the steam pressure or vacuum to be used for the corresponding temperature.

The general operation of the system may now be followed. It will be noted first that the lowermost contact in the series 52 is marked F. and the uppermost contact 52 is marked 65 F. This is the range over which the outside temperature control is efiective. At 0 and below, all steam supplied will be at 212 F. and at a temperature above 65 the automatic regulation will go or? as hereinafter described. The corresponding contacts of the series 48 has the lower contact marked 0 pounds and the upper contact marked inches. This is the range of vacuum over which the system operates. The 0 temperature contact is connected to the 0 pounds contact, and the 65 contact is connected to the 25 inches contact. Thus it will appear that when the weather is coldest the highest absolute pressure will exist in the system which wil1 be a pressure of approximately 0 pounds atmosphere, and when the outside temperature is warm the highest degree of vacuum in the system will be reached.

' In the operation, assuming the presence of steam in the supply line 2! up to the valve 25 and the starting up of the heating cycle, the switch 5! is closed. Assume that the outside temperature is at approximately the midpoint between 0 and 65, or around 32 F. Under these conditions a circuit will be closed to the electromagnet 23 to start the pump is into operation. In starting up the system the arm 56 will point At 66 is a presvacuum in the system at this time. However, because of the extended brush being extended a live contact opposite the arm 54 will be engaged (assuming the outside temperature to be below F.) and the pump motor will be operated. At this time the spring 4| will be holding the valve 26 open. The operation of the vacuum pump will exhaust the gases in the heating system and steam will be circulated through it. In order for the vacuum pump to overcome the friction to the flow of gases through the system, it must exert a fairly high suction. When the steam is drawn through the system to the check valve l4 there will be a differential of pressure due to the presence of steam on the one side of the valve as against the absence of fluid pressure on the other which will cause the valve to close and the steam cannot pass this point. The suction pump, however, may continue to operate but when a predetermined degree of vacuum is reached the motor 36 will operate to close the valve and the motor 45 will operate to raise the brush All above the live contact opposite brush 53 to break the circuit to the relay switch. Thus the steam will be out oif and the pump will be stopped. As the steam cools down the suction in the system will begin to decrease, and as this takes place the arm 46 will move down until it again engages I a live contact when the suction pump will again toward the 0 pound contact, as there will be no be operated. Likewise as the suction in the systern decreases the arm 32 will be drawn up under the action of the spring 4| admitting additional steam to the system. Once the system has been set into operation, it will automatically respond to variations in the outside temperature. If outside temperature drops to 0, the brush .53 will. move down to 0 contact. This means at this the pressure in the system will be substantially atmospheric pressure so that the brush fa? will be drawn down by its spring to the lowermost contact. Actually the pump I8 will work only sufficiently to overcome the frictional resistance of the circulating system. If the pressure in the radiators tends to build up due to the valve 2-5 being open to a pressure above atmospheric pressure, the pump will continue to operate and the diiierential check valve [5 will close, whereupon the pump will continue to draw a vacuum in the line 42, tending to lift the brush 4! from the live contact and also tending to operate the expansible chamber motor 36 to .close the valve 25. Be-

cause the suction is communicated to expansion chamber motors 36 and 45 directly through suction line 42, without the intervening effects of the friction of the heating system, these motors will begin to respond before too high a vacuum is created in the heating system so that steam will at no time enter the system at too high a rate. In other words, as suction increases to pull steam more rapidly through valve 25, motor as operates to gradually close this valve. As the outside ternperature rises and the brush 53 moves up the series of contacts, a higher degree of vacuum must be maintained in the system to reduce the temperature of the steam, so that when the brush '53 is on the uppermost contact 52 and the uppermost contact 48 is then the live contact, the mo tor l8 will operate almost continuously to maintain the maximum vacuum in the system. When the vacuum exceeds 25 inches the brush 4! will be drawn up from the live contact 48 to break the motor circuit. Even though the pump i'l is being operated most of the time, steam is not drawn out of the system, first, because the valve 25 is closed, or nearly closed, most of the time,

and second, because when the steam reaches: the biased check valve l4, this valve will close. As stated above, this valve is biased to close when there is'a predetermined differential pressure on opposite sides of the valve. When there is a vacuum on both sides the valve, of course, remains open, but when the space has been filled with steam on the inner side of the valve the flow of steam through the valve tends to close it. The biasing force I 5 on the valve [4 is suflicient to overcome the frictional resistance of drawing a vacuum through the heating system to the inlet side thereof. In order to prevent the pulling of an excessively high vacuum in the system, there may be a relief valve in the line 42 in the form of an inwardly opening check valve 69 which is biased to resist opening until a predetermined vacuum has been reached in the system.

It may sometimes happen that the in-rush of steam into the cold radiators will tend to create a high vacuum in the system. This high vac uum would, until the motor 36 could be energized to close the valve 26, causean excess of steam to surge intothe inlet side of the system. The check valve 43 in the suction pipe 42 prevents this by reason of the fact that if the suction in the manifold 25 is higher than the suction in the pipe 42, the check valve 43 will open, establishing continuous communication from the inlet side of the system to the outlet side at a point close to the pump. This would tend to equalize the pressures on the inlet and outlet sides and it will also tend to communicate the increased suction directly from the intake side of the system to the expansible chamber motor 36 to cause the operation of this motor to close the steam valve 26.

By reference to Figure 2 it will be noted that the steam valve 26, being of a double ported type, is equally balanced against being opened by either pressure or suction. In other words, pressure tending to unseat the valve from one port tends equally to seat the valve for the other port, thus balancing the two forces, and the expansion chamber motor 36 acts only in opposition to the spring 4|. This allows for very close adjustment in the operation of the valve.

When the outside temperature rises about 65, or above such predetermined maximum as may be established, the operation of the heating system is no longer required, and my invention provides means for cutting out the automatic control when such predetermined maximum outside temperature is reached. This is accomplished by means of the contact 56 at the top of the series of contacts 52. When the temperature arm 54 is moved beyond the last contact 52 onto the contact 56, it closes a circuit from the wire 59 through the wire 62, brush 53, contact 56, and wire 18 to electromagnet means such as solenoid H for depressing an arm 72, forcing this arm down against the terminal 3| of the valve stem 29 to close the valve 26. The return circuit from the solenoid II is through wire 13 to current supply line 68. The automatic system may also be rendered manually ineffective by opening the switch 8| and closing the switch 14 from the line 59, to wire 15 leading to the solenoid II, the return circuit in this case also being the wire 13.

This opening of the switch BI and the closing of the switch 14 may be accomplished by the operator at any time, usually when the system goes from an automatic day operation to a night heating program. Once the solenoid 1| has been-energized'to close the valve 26, the valve will stay closed. If the switch 6| has not been opened, decrease in the outside temperatures will reestablish automatic regulation as soon as the brush 53 moves down onto one of the contacts 52.

From the foregoing description it will be seen that as long as the system is under automatic control there will be steam in the radiators or other heat transfer elements 3 but the tempera ture of the steam will be raised or lowered, depending upon the degree of vacuum maintained in the system, and the amount of heat demanded by the prevailing outside temperature.

The reason for providing a slight relative movement between the arms 46 and 54, and their respective brushes 41 and 53, is to permit these arms to move back and forth to a limited extent without changing the position of the contacts. For example, a change of tWo or three degrees in the outside temperature might take place without the shifting of a brush to another contact.

It is contemplated that instead of there being fully automatic control there may be a manual control or there may be a combined manual and automatic control with means for taking over the manual operation should the automatic mechanism fail to properly function. Figure '7 shows a form of valve which may be employeo for either automatic or manual operation. In this form of valve, the valve generally is designated I6 and it comprises a valve body 11 with opposed valve ports 18 and 19. The valve stem has a fixed upper valve 8| thereon, which has no relative movement with respect to the valve stem and a lower valve element 82 with which the valve stem is slidably connected, the arrangement being such that the valve stem may have a limited movement with respect to the valve 82. With this arrangement the presence of steam Lmder pressure on the inlet side of the valve, designated by the inlet pipe 83, above the pressure on the outlet side of the valve designated by the outlet pipe 84 will tend to lift the valve 8| from its seat, and since this valve can move relatively to the valve 82, the valve 82 will offer no opposition to counteract the movement of the valve 8 I. When the valve stem 80 moves a predetermined distance, however, the valve 82 will then be lifted from its seat to increase the total passageway through the valve. The valve stem 8|) is provided with a terminal 85. There is a pivoted lever 86 with an abutment 81 which engages this terminal 85. At 88 there is shown an expansible motor corresponding to the motor 3'! of Figure 3, this motor having an extension 89 that is connected to one end of the lever 86 at 90. This connection may be in the form of a pin or bolt which can easily be removed to transfer from automatic to manual operation. On the opposite end of the lever 86 from the motor 88 is an adjustable counterweight 9|.

In operation the counterweight 9| may tend to normally keep the valve 8| on its seat until there is a predetermined differential of pressure on the inlet and outlet sides. It is contemplated that in a system using this valve the motor 88 would be included in a line corresponding to the suction line 4240 of Figure 1 so that the suction in the system acts in conjunction with the weight 9| to keep the valve 8| seated. If the system is to be put on manual operation, the connection 90 between the motor element 89 and the lever 86 is removed and the weight 9| is adjusted further out toward the end of the lever 86, de-

pending upon the difi'erential of pressure which is to be maintained before the valve 8| opens. For example, if steam on the inlet side is supplied at 10 pounds whereas the outside temperature indicator 65 of Figure 1 may indicate that 5 inches of vacuum should be maintained in the system for the then prevailing outside temperature, the Weight 9| is adjusted so that the valve 8| will not open until the vacuum in the pipe 84 is 5 inches or greater. If the weather is warmer, requiring a still higher vacuum on the outlet side, the weight 9! is adjusted still further out along the lever 86. In the manual system of operation the operator watches the gauge 65 and sets the counterweight 9| accordingly.

My invention provides an apparatus and method wherein a steam heating system is always operated at 0 or negative pressure and wherein the temperature of steam in the radiators is varied between a maximum of 212 and a minimum of 132, according to variations in the outside temperature.

While I have illustrated and described certain specific embodiments of my invention, it will be understood that this is merely by way of illustration and that various changes and modifications may be made in the construction and arrangement of parts within the contemplation of my invention and under the scope of the following claims.

I claim:

1. Heating apparatus comprising a supply line having steam under pressure therein, a heat transfer system having an inlet connected to the supply line and having an outlet, asuction pump connected with the outlet, electric switching means responsive to the vacuum in the system and to outside temperature to control the suction pump, a valve in the supply line, and means responsive to suction in the system for controlling the operation of the valve.

2. A heating apparatus comprising a supply line for supplying steam, a heat transfer system having an inlet connected to the supply line and having an outlet, a suction pump connected to the outlet, electric switching means responsive to vacuum in the system coupled with means responsive to ambient temperature for controlling the operation of the suction pump, a valve in the supply line, and an expansible chamber motor communicating with the suction pump for controlling the operation of said valve.

3. A heating apparatus comprising a steam supply line, a heat transfer system having an inlet side connected to the supply line and having an outlet side, a suction pump connected with the outlet side of the system, a check valve between the system and the pump opening toward the system and biased to remain open until a predetermined differential of pressure on opposite sides of the valve is created, a supply valve between the inlet pipe and the system, and means connected with the vacuum pump for controlling said supply valve according to the vacuum in the system.

4. In a vacuum heating system having a vacuum pump, a motor for driving the pump and a control for the motor comprising a series of contacts, brush means movable over said series of contacts, means responsive to ambient temperature for moving the brush means, a second series of contacts connected in series with the corresponding contacts of the first series, and brush means movable over the second series of contacts, means responsive to vacuum in the system for moving the second brush means and a motor controlled circuit for said pump driving motor including both of said brush means and the contacts with which they cooperate.

5. A vacuum heating apparatus comprising a heating system, a steam supply line for the heating system, a suction line leading from the heating system, a suction pump in said suction line for exhausting gases from the system, an inwardly open outwardly closing check valve inthe suction line between the heating system and the pump, a steam supply valve in the steam supply line, and means coupled into the suction line between said check valve and said pump and coupled into the supply line between said valve and the heating units comprising a pipe line with a check valve that closes in the direction of the suction pump for communicating abnormally low pressures in the supply side of the line to the suction side of the line. v

6. A vacuum heating apparatus comprising a heating system with heating units, a steam supply line for the heating system, a suction line leading from the heating system, a suction pump in said suction line for exhausting gases from the system, an inwardly open outwardly closing check valve in the suction line between the heating system and the pump, a steam supply valve in the steam supply line, means coupled into the suction line between said check valve and said pump and coupled into the supply line between said valve and the heating units comprisinga pipe line with a check valve that closes in the direction of the suction pump for communicating abnormally low pressures in the supply side of the line to the suction side of the line, and an expansion chamber motor connected into said line between said last-named check valve and the suction pump for operating the supply valve arranged to close the supply valve upon a predetermined decrease of pressure in the system.

'7. A vacuum heating apparatus comprising a heating system with heating units, a steam supply line for the heating system, a suction line leading from the heating system, a suction pump in said suction line for exhausting gases from the system, an inwardly open outwardly closing check valve in the suction line between the heating system and the pump, a steam supply valve in the steam supply line, means coupled into the suction line between said check valve and said pump and coupled into the supply line between said valve and the heating units comprising a pipe line with a check valve that closes in the direction of the suction pump for communicating abnormally low pressures in the supply side of the line to the suction side of the line, an expansion chamber motor connected into said line between said lastnamed check valve and the suction pump for operating the supply valve, and variable contact apparatus also connected into said line between the last-named check valve and the suction pump for selectively engaging one of several contacts according to the vacuum in the system arranged to close the supply valve upon a predetermined decrease of pressure in the system.

8. A vacuum heating apparatus comprising .a heating system with heating units, a steam supply line for the heating system, a suction line leading from the heating system, a suction pump in said suction line for exhausting gases from the system, an inwardly open outwardly closing check valve in the suction line between the heating system and the pump, a steam supply valve in the steam supply line, means coupled into the suction line between said check valve and said pump and coupled into the supply line between said valve and the heating units comprising a pipe line with a check valve that closes in the direction of the suction pump for communicating abnormally low pressures in the supply side of the line to the suction side of the line, an expansion chamber motor connected into said line between said lastnamed check valve and the suction pump for operating the supply valve, variable contact apparatus also connected into said line between the last-named check valve and the suction pump for selectively engaging one of several contacts according to the vacuum in the system, and a thermally responsive circuit closer for selectively energizing said contacts according to variations in outside temperature arranged to close the supply valve upon a predetermined decrease of pressure inthe system.

9. A heating apparatus of the class described comprising a heat exchange system having inlet and outlet sides, a steam supply line connected to the inlet side, a suction pump connected with the outlet side, means controlling the operation of the suction pump to maintain a variable degree of vacuum in the system, an inlet valve in the supply line for controlling the flow of steam into the system, biasing means tending to operate the valve to an open position, and means responsive to vacuum in the system for holding the valve closed until the. predetermined condition of vacuum obtains in the system.

10. A heating apparatus of the class described comprising a heat exchange system having inlet and outlet sides, a steam supply line connected to the inlet side, a suction pump connected with the outlet side, means controlling the operation of the suction pump to maintain a variable debefore the valve opens.

the supply line for controlling the flow of steam into the system, said valve being. arranged to open when the pressure on the inlet side exceeds the pressure on the outlet side,. and adjustable biasing means for the valve for oontrollably regulating the difierential pressure which must exist 11. A heating system having a steam inlet pi and an exhaust pipe, a suction pump connected with the exhaust pipe, a valve in the inlet pipe, a motor for driving the suction pump, a composite electric switching device including a means actuated by changes in outside temperature and an expansible chamber motor means connected into the heating system controlling the motor and responsive jointly to prevailing outside tem perature and the degree of vacuum in the system whereby the degree of vacuum in the system will vary according to prevailing temperatures, and means for operating the valve in the inlet pipe to vary the supply of steam inversely to the degree of vacuum.

12. A heating system having a steam inlet pipe and an exhaust pipe, a suction pump connected with the exhaust pipe, a valve in the inlet pipe, a motor for driving the suction pump, a composite electric switching device including an outside temperature actuated means and an expansible chamber motor means connected into the system for controlling the motor and responsive jointly to prevailing outside temperature and the degree of vacuum in the system whereby the degree of vacuum in the system will vary according to prevailing temperatures, and means responsive to the vacuum in the system to vary the BERNARD J. INGRAM. 

